A motor may transmit rotational force of a rotor to a shaft that drives a load. For example, the shaft may be connected to a drum of a washing machine and be configured to drive the drum. As another example, the shaft may be connected to a fan of a refrigerator and be configured to drive the fan to supply cold air to cool a space. In some examples, the motor may be used in a compressor to compress refrigerant.
A rotor is rotatable in a motor by an electromagnetic interaction with a stator. For example, a coil may be wounded around the stator, and the rotor may rotate with respect to the stator as an electric current is applied to the coil.
The stator may include a stator core, and the stator core may be made of a conductor. In some examples, the stator may be fixed to an object such as a motor housing, a motor bracket, or a tub of a washing machine by another coupling structure for fixing the stator to the object.
The rotor may have various types including a permanent magnet type.
For example, the permanent magnet type rotor may include a SPM (Surface Permanent Magnet) type rotor in which a permanent magnet is arranged in an outer circumferential surface of the rotor, and an IPM (Interior Permanent Magnet) type rotor in which a permanent magnet is arranged in the rotor. The SPM rotor uses only a magnetic torque generated by the permanent magnet. The IPM rotor may use not only the magnetic torque but also a reluctance torque generated by a magnetic resistance difference. The IPM type rotor may accompany an increase of the manufacturing cost, while having a wider operation area.
The IPM motor may include a spoke type permanent magnet motor. In the spoke type permanent magnet motor, permanent magnets are embedded in both ends of one pole in symmetry. A magnetic polarity may be formed by a structure including a core surface between the permanent magnetics. An increase of gap flux density may generate a high torque and a high output. In some cases, an advantage of the IPM motor may include a slim motor design for the same output and a high price competitiveness.
FIG. 1 illustrates a conventional spoke type permanent magnet motor in the related art.
The motor 1 includes a stator 10 and a rotor 20.
The stator 10 may include a stator core 11, and a plurality of teeth 12 projected from the stator core 11 in a radial direction. The stator core 11 may be formed in a ring shape.
A pole shoe 13 extends from an inner radial end of the teeth 12 in both circumferential directions. A slot 14 is formed between two teeth so that the coil may be wounded by the teeth and the slot 14.
The rotor 20 includes a rotor core. The rotor core has an outer diameter core 21, an inner diameter core 22, and an inner diameter connecting portion 40. A permanent magnet loading portion 24 may be formed in the outer diameter core 21, and a permanent magnet 25 longitudinally may be loaded in the permanent magnet loading portion 24 in a radial direction. The outer diameter core 21 may be referred to as the outer core, and the inner diameter core 22 may be referred to as the inner core, because the inner diameter core 22 is located in an inner area with respect to a radial direction of the outer diameter core 21.
In some examples, the permanent magnet 25 may be loaded in a circumferential direction, and a gap 30 may be formed in the outer diameter core 21 between the permanent magnets 25. The loading directions of the permanent magnets facing each other in the circumferential direction are in opposite.
Loading projections 31 may be formed inside and outside of the permanent magnet loading portion 24 with respect to the radial direction.
Connection gaps 27 and 29 may be formed between the outer diameter core 21 and the inner diameter core 22. The rotor core is integrally formed as one body so that a radial rib 26 may connect the outer diameter core 21 and the inner diameter core 22 to each other and cross the connection gaps 27 and 29 in a radial direction. A circumferential rib 28 may be formed in a middle area of the radial rib 26. The inner diameter connecting portion 40 may include the radial rib 26 and the circumferential rib 28.
The circumferential rib 28 may partition the gap into the connection gaps in the radial direction, specifically, the outer connection gap 27 and the inner connection gap 29 that is located radially inward of the outer connection gap 27.
A shaft hole 23 configured to receive the shaft may be formed in the center of the inner diameter core 22.
In the spoke type motor, the coordinate system expressed as three phases of U, V and W may be converted into D-Q axis rectangular coordinates to show the physical quantity of the motor by using two variables and perform the instantaneous control.
For example, the D-axis is an axis for generating the magnetic flux of the motor and is set as a direction of the magnetic flux generated in the U-axis winding. Accordingly, D-axis may be a reference axis of vector control.
The Q-axis is orthogonal to the D-axis as the axis of the currents which generates a torque in the vector control. Accordingly, the Q-axis is controlled in case of controlling currents.
For example, the center axis of the rotor core (e.g., an axis extending from the center of the rotor to a circumferential center of the rotor core) may be the D-axis, and the center axis of the permanent magnet (e.g., an axis extending from the center of the rotor to a circumferential center of the permanent magnet) may be the Q-axis.
The inner diameter connecting portion 40, for example, the radial rib 26 is located on the D-axis in the spoke type motor shown in FIG. 1. In this case, the thickness of the radial rib 26 affects the flux leakage and the mechanical rigidity. For example, as a circumferential-direction width the radial rib 26 becomes thicker and thicker, more flux leakage, which may be irrelevant to the performance of the motor, may be generated and deteriorate the efficiency of the motor, but the mechanical rigidity for connecting the outer diameter core 21 and the inner diameter core 22 with each other may be enhanced. Accordingly, the damage or breakage to the rotor caused by the twisting may be reduced.
FIGS. 2 and 3, respectively, show a diagram and a saturation degree of the magnetic flux in the inner diameter connecting portion 40 of the rotor shown in FIG. 1.
The leakage flux generated in the permanent magnets arranged in both sides with respect to the radial rib 26 may pass through the radial rib. The saturation degree of the magnetic flux in the radial rib becomes high, because the leakage flux generated by the two permanent magnets 25 passes through a one radial rib 26. The leakage flux in the circumferential rib 28 and the inner diameter core 22 is distributed to two sides and the saturation degree of the magnetic flux in the core becomes low.
As shown in FIGS. 2 and 3, the amount of the leakage flux is variable according to the thickness (e.g., a circumferential width) of the radial rib 26. For example, as the radial rib 26 becomes thicker in the circumferential direction, the quantity of the leakage flux may increase. As the radial rib 26 becomes thinner, the mechanical rigidity may become noticeably low. In this example, the quantity of the leakage flux and the mechanical rigidity are related in an inverse proportion to each other.
While magnetic flux saturation is generated in the radial rib 26, magnetic flux is not saturated in the portion between the circumferential rib 28 and the inner diameter core 22 and in the inner diameter core 22. For example, not an entire are of the leakage flux movement passage is saturated. Accordingly, the leakage flux may be consistently generated, and which may not minimize the quantity of the leakage flux.
In other examples, a motor may include an inner diameter connecting portion in which the radial rib 26 is formed not in the D-axis but in the Q-axis.
For example, a spoke type motor may include a radial rib and connection bridges connected with both ends of the radial rib. The mechanical rigidity may be reinforced somewhat, but one more leakage flux passage is formed. While the radial rib located in a lower end of a permanent magnet becomes thicker, the mechanical rigidity may be reinforced, but the leakage flux passage becomes larger enough to increase the quantity of the leakage flux.
FIGS. 4 and 5, respectively, show a diagram of magnetic flux and a saturation degree of the magnetic flux in the inner diameter connecting portion in a related art.
As shown in the drawings, the inner diameter connecting portion 340 extends outwardly with respect to a radial direction, and includes the radial rib 326 that supports a center area of the permanent magnet 325, and extension ribs 327 formed in left and right areas of the radial rib 326. The extension rib 327 is curved to make a magnetic circuit become long. In this case, the magnetic resistance may be increased. There is a space 331 between the inner diameter connecting portions 340.
The radial rib 326 extends to contact with a radial inner surface of the permanent magnet 325 so that a predetermined area of the radial rib 326 may be located in an outer portion in a radial direction with respect to the extension rib 327.
The magnetic flux saturation degree of the leakage flux moving passage may be variable according to the thickness of the radial rib 326.
The magnetic flux may flow from one end of the extension rib 327 to the other end of the extension rib 327 opposite to the one end, after passing the radial rib 326. As shown in the drawing, the magnetic flux saturation is generated only in the extension rib 327, not in the radial rib 326 arranged between the extension ribs 327. Accordingly, the leakage flux is consistently generated and it may be limited to minimize the quantity of the leakage flux because the entire area of the leakage flux moving passage is not saturated.
FIGS. 6 and 7, respectively, show a diagram of magnetic flux and a saturation degree of the magnetic flux in the inner diameter connecting portion in another related art. In this example, supporting ribs 328 are further provided in both sides of the radial rib 326 to reinforce the strength of the inner diameter connecting portion.
In this example, the magnetic flux saturation degree of the leakage flux moving passage is variable according to the thickness of the radial rib 326.
The magnetic flux flows from one extension rib 327 to the other extension rib 327 after passing the radial rib 326. The magnetic flux flows from one supporting rib 328 to the other supporting rib 328, after passing the radial rib 326.
As shown in the drawings, the magnetic flux saturation is generated only in the extension ribs 327 and the supporting ribs 328, not in the radial rib 326 provided between them. Accordingly, the entire leakage flux moving passage is not saturated so that the leakage flux may be consistently generated and it may be limited to minimize the quantity of the leakage flux.
Accordingly, it may be of interest to provide a motor (e.g., a spoke type motor), which is capable of enhancing the motor efficiency by minimizing the leakage flux and also reinforcing the mechanical rigidity.